Borate speciation and structural studies of vanadium ion doping in borate bioglass

Abstract

Different glasses in the system, xV2O5-(45–x)B2O3–24.5Na2O–24.5CaO–6P2O5, (x = 0, 3, 6, 9, 12, 15, 18, 20 and 25 Wt%) were prepared through melt quenching method. X-ray diffraction (XRD) patterns have revealed that the amorphous structure is the dominant type. There is no tendency for crystallization even with higher vanadium content. Crystallization occurred utilizing treating the glasses thermally. FTIR spectral absorption data showed the presence of both BO3 and BO4 structural groups in combination with the presence of VO4 and VO5 structural building units. The deconvolution analysis technique (DAT) was adopted to retrace the conversion progressions of the coordinated boron. At low V2O5 content (up to 10 wt%), it entered as a glass modifier as well as both Na2O and CaO. The high content of the glass modifier (Na2O + CaO + V2O5) could destroy some of the well-formed BO4 units which are transformed into asymmetric BO3. The back conversion of BO4 to asymmetric or loose BO3 can simply reduce the fraction of tetrahedral units (N4). When V2O5 entered as a glass former (> 10 wt%), the N4 fraction increased. The change in the measured densities and estimated molar volumes may assigned to the formation of BO4 units resulting from increasing vanadium oxide content.